This proposal is for funds to continue studies on the normal organization of the hippocampus and the reorganization which take splace after lesions to its major afferents. Experiments will be carried out in intact and lesioned rats and in hippocampal explants prepared from these animals. Three groups of studies are planned. On the first we will attempt to improve our current explant techniques by building a better recording chamber, extending the life-span of the explants, and developing techniques for tracing axonal connection in the explants. The second set of experiments will investigate the physiology of the septo-denatate gyrus system and will correlate cell physiology with cell structure in the hippo-campus using single cell labelling techniques. The third group of projects will: 1) provide a time course for axon sprouting in hippocampus, 2) study sprouting at the electron microscopic level, 3) investigate an area in which we have been unable to detect sprouting in earlier work, and 4) attempt to manipulate sprouting with electrical stimulation. The overal goal of these projects is to provide a better understanding of the mechanisms underlying morphological plasticity in the mammalian brain.